1. Field of the Invention
This invention relates to interleaving materials for separating glass sheets and protecting them from scratching and straining, and to a process for protecting such glass sheets during storage or transport, particularly when stacked in conventional manner. References in this specification to "stacked glass sheets" or to a "stack of glass sheets" are to be understood to refer to an assemblage of a plurality of glass sheets whose major surfaces are in adjacent face-to-face relationship, irrespective of whether those major surfaces are disposed horizontally or vertically or in an intermediate inclined position.
During storage and transit, stacked glass sheets are liable to deteriorate in two principal ways, particularly if they are allowed to come into contact with one another. Relative movement between adjacent sheets is liable to cause scratching of the adjacent glass surfaces. There is also a tendency for a stain to develop on the facing glass surfaces of adjacent sheets, particularly in hot, humid conditions. Staining is thus a particular problem in climates where such conditions are common, but it can also be a significant problem in more temperate climates.
2. Description of the Prior Art
It is known to protect stacked glass sheets from scratching by disposing paper sheets or powder, for example a powder formed of small plastics beads or of wood flour, between adjacent glass sheets. Such paper sheets and powder are known as "interleaving materials". It has also been proposed in British patent specification No. 861,578 to protect sheet glass against iridescence (i.e. staining) by the use of a slightly acid agent (preferably sodium bisulphate but alternatively another acid reacting salt or even a weak acid such as citric acid) which may be incorporated by absorption into or adsorption on an inert material acting as a support, it being possible for the latter to be in the form of a powder or of a sheet which is placed against the glass surfaces. The inert materials acting as support are neutral or very slightly acid mineral or vegetable products, such as sawdust and cellulose products.
In U.S. Pat. Spec. No. 3,723,312, an interleaving material is proposed which comprises a dedusted agglomerated organic acid, specifically salicylic acid, mixed with an inert particulate separating material such as wood flour, polystyrene or Lucite (a methyl methacrylate polymer), the particles of which are preferably smaller than the particles of the acid. It is stated in the U.S. Specification that acids impregnated into porous solid inert separator materials perform less suitably than agglomerated acids.